Automated transmissions have long been used in various types of motor vehicles. The shifting movements for engaging gears, for actuating clutches and transmission brakes, are usually effected by pressure-medium-actuated control cylinders.
Such transmissions at least in part use the reservoir pressure of a vehicle in which they are fitted. The shifting elements, i.e. the main cut-off valves and the shifting valves arranged downstream therefrom, are either connected directly to this reservoir pressure or system pressure of the vehicle, or supplied with a constant operating pressure that is reduced for example by pressure-reducing valves or the like. This means that the loading of the shifting elements, the shifting times, the shifting noise, etc., cannot be influenced or can only be so to a small extent. Particularly in the case of transmission brakes, the problem arises that their function is affected by a production-related scatter, so that their control is problematic and the reliability and precision desired for efficient shifting cannot always be achieved.
From DE 10 2008 001 686 A1 a method for controlling shifts in an automated change-speed transmission is already known, in which the function of a transmission brake with a substantially constant braking torque is assisted by briefly closing the automatically controllable separator clutch in the event of a deviation from a nominal value caused for example by current environmental or operating temperatures or by the wear condition of the friction linings. However, this measure does not make it possible to determine and modulate the current actual braking torque or its deviation from the nominal braking torque.